This invention relates to semiconductor optical devices, including lasers and electroabsorption modulators, and detectors.
Electroabsorption modulated laser (EML) devices have recently received a great deal of attention for use in high speed optical systems. Such devices typically include a semiconductor laser and modulator found in a single substrate. These devices usually include a semiconductor multi quantum well (MQW) active region, a contact layer formed thereover to facilitate electrical contact with the active layer, a current blocking layer for directing current to the active region, and a cladding layer to confine light to the active region. Zn is a commonly used p-type dopant for the blocking, contact and cladding layers, and the performance of the laser and modulator depends critically on the level of Zn in the various layers of the device.
It is desired to maintain a certain Zn dopant profile in the device structure for optimum performance. However, the Zn profile in the blocking and cladding layers may get modified during the growth of the contact layer due to the migration of the Zn dopant from the contact layer. One solution to the problem is to reduce the amount of Zn in the cladding, blocking, and contact layers. However, this approach also adversely affects other device properties, such as total device resistance.
It is desirable, therefore, to provide a process and resulting device which mitigate the problem of Zn migration in optical devices.